Metal containers such as collapsible tubes used for pharmaceutical preparations, cosmetics, food, household and other products are sold throughout the world and are required to be decorated and printed with information. To decorate such containers with product information, etc., offset printing directly onto the containers (or onto an enamel coating on the containers) is normally used. However, this limits the quality, diversity and complexity of the print material (i.e. the design matter) because offset printing techniques are themselves so limited. Moreover, offset printing requires that lengthy set-up and change over procedures be conducted to implement a new design or change from one design to another.
Some product manufacturers require metal containers for products distributed to different countries each of which may have different marking requirements (i.e. due to national language and other differences). Often, relatively small shipments to any given foreign country are made at one time. Currently, manufacturers of such containers require the purchase of minimum orders (typically 10,000 units) of preprinted containers which must then be kept in inventory until required or discarded when rendered obsolete due to packaging changes. Often the minimum order is much more than a purchaser's requirements and the majority of the containers are scrapped.
To avoid such waste, it is desirable to print only the number of containers which are required at any given time. However, the cost to a container manufacturer to produce such small numbers of printed containers is prohibitive due to the cumbersome set-up procedures associated with offset printers which are most efficiently operated on a mass-production assembly line. Presently, collapsible containers of the type contemplated are normally produced in an assembly line which forms the container from raw materials such as an aluminum slug; coats the container's exterior with a polyester enamel which bonds to the surface of the container and provides an aesthetic appearance and accepts printing inks; prints material onto the container using offset printing techniques; cures the printed, enameled container; and, applies a cap to the top end of the container (the other end being left open for filling with product by the purchaser). The production line downtime required to configure the line, particularly the offset printing system, is the same for short runs as for longer runs. Thus, it is inefficient to produce shorter production runs.
An alternative to printing directly on the metal containers is to apply pre-printed labels to the containers but present labeling methods are not acceptable to a number of different industrial purchasers due to the lack of security associated with the labels applied by such methods. Typically, such methods use labels having a thin printed substrate and an adhesive backing layer and suffer the following disadvantages:
(a) The labels will not withstand the physical abuse, such as squeezing and crinkling, to which collapsible containers may be subjected by the public; PA1 (b) The chemical contents of the container may react with the standard adhesive systems used to apply such labels, thereby potentially causing the adhesive to fail and the label to fall off; and, PA1 (c) Because the labels do not bond to the container they can be selectively removed from the container with solvents or other means leaving no evidence of tampering (and this is unacceptable to manufacturers facing potential product liability claims).
Adhesive labels (i.e. labels having a substrate, a print layer and an adhesive layer) are known in the art and are commonly used for decorating plastic containers. For example, Canadian Patent No. 1,259,183 issued on Sep. 12, 1989 provides such a label having an adhesive backing which bonds to the container. However, a disadvantage associated with adhesive-backed labels is that they require that certain handling and storage conditions be met so as to avoid compromising the adhesive prior to use. Moreover, such labels which are presently available do not accomplish bonding with a metal container.
It is also known to apply metallic layers or labels to metal surfaces having finish coatings thereon by using a transfer sheet, the transfer sheet having on it the metallic layer and an adhesive layer thereover and a release layer and releasable backing sheet thereunder. For example, U.S. Pat. No. 3,340,121 issued Dec. 20, 1963 provides for such a transfer sheet which is applied by heating the metal surface to a temperature at which the release layer is activated and the adhesive softens and then pressing the transfer sheet against the hot metal surface until the release layer is activated and the backing sheet can be removed after which time the metallic layer is adhered to the metal surface (the adhesive layer and finish coating being compatible). Such transfer sheets also have associated with them the disadvantage of structural complexity and handling and storage requirements and restrictions.
Also known is the method provided by U.S. Pat. No. 3,553,044 issued Jan. 5, 1971 for incorporating a decal as an integral part of a coating on a surface whereby a decal is printed onto a solvent soluble polymeric base, the decal-printed base is attached to the surface and a clear solvent-containing coating is applied over the base and surface so that the base is dissolved and the decal becomes an integral part of the coating. However, the use of such a solvent-based coating is unacceptable for many applications as is the need to coat the applied decal.
Therefore, it is desirable to provide a method of applying pre-printed graphic labels to metal containers which will render the label an integral part of the container and able to pass rigorous product handling tests such as the "crinkle test" by which the container is repeatedly bent in different directions and crinkled to ensure that the label remains intact and does not peel or break off from the container. It is also desirable to provide such a method that is conducive to short production runs of containers.